Mineral wool composition

ABSTRACT

The subject of the invention is a mineral wool capable of being dissolved in a physiological medium and comprising the constituents below in the following percentages by weight: 
     
       
         
               
               
               
             
                   
                   
               
                   
                 SiO 2   
                 38-52% 
               
                   
                 Al 2 O 3   
                 16-23% 
               
                   
                 RO (CaO + MgO) 
                 4-15% 
               
                   
                 R 2 O (Na 2 O + K 2 O) 
                 16-25% 
               
                   
                 B 2 O 3   
                 0-10% 
               
                   
                 Fe 2 O 3  (total iron) 
                 0-3%, preferably 0-1.5% 
               
                   
                 P 2 O 5   
                 0-3%, preferably 0-1.5% 
               
                   
                 TiO 2   
                 0-2%.

The present invention relates to the field of artificial mineral wool.It is aimed more particularly at mineral wool intended for manufacturingthermal and/or acoustic insulation materials or soilless-culturesubstrates.

It concerns more particularly mineral wool of the glass wool type.

This type of mineral wool is usually fiberized by so-called “internal”centrifuging processes, i.e. those using centrifugers rotating at highspeed and filled with holes. They are in fact well suited to fiberizingmineral wool of the glass wool type, broadly having a compositionrelatively rich in alkaline metal oxides and having a lower liquidustemperature and a higher viscosity at the fiberizing temperature thanrock wool or basalt wool. This type of process is described inparticular in Patents EP-0 189 354 or EP-0 519 797.

To the known criteria of industrial and economic feasibility and ofquality level have in recent years been added that of biodegradabilityof mineral wool, namely its ability to be rapidly dissolved in aphysiological medium, so as to prevent any potential pathogenic riskassociated with the possible accumulation of the finest fibres in thebody by inhalation.

The object of the invention is therefore to improve the chemicalcomposition of mineral wool, especially of the glass wool type, theimprovement being aimed especially at increasing its biodegradabilityand/or at reconciling biodegradability with ability to be fiberized byinternal centrifuging (without, however, excluding other fiberizingmethods).

The subject of the invention is a mineral wool capable of beingdissolved in a physiological medium, which comprises the constituentsbelow in the following percentages by weight:

SiO₂ 38-52%, preferably at least 40%, especially 41-48% or 45-50% Al₂O₃16-23%, preferably 17-21% or 17-20% RO (CaO and/or MgO) 4-15%,preferably 5-12% or 5-11% R₂O (Na₂O and/or K₂O) 16-25%, preferably17-22% or 1720% B₂O₃ 0-10%, especially at least 1%, preferably 3- 9% or4-10% P₂O₅ 0-3%, preferably 0-1.5%, especially 0 or greater than 0 andat most 0.5% Fe₂O₃ (total iron) 0-3%, preferably 0-1.5%, especiallyabout 0.01 to 1% TiO₂ 0-2%

(Throughout the rest of the text, any percentage of a constituent of thecomposition should be understood to mean a percentage by weight).

The selection of such a composition has allowed a whole graph ofadvantages to be built up, especially by varying the many complex rolesthat a number of its specific constituents play.

Thus, what is involved is a mineral wool composition of the glass-wooltype, in which its content of alkali metal oxides (R₂O) essentially inthe form of Na₂O and/or K₂O is greater than its content ofalkaline-earth metal oxides (RO), which is essentially in the form ofCaO and/or MgO. The content of iron oxide (measured in the form ofFe₂O₃, but corresponding, by convention, to the total iron content) isvery moderate or even zero; on the other hand, the boron oxide contentis significant.

The viscosity at fiberizing of such a composition is suitable forinternal centrifuging.

As regards biodegradability, it was already known that certain compoundssuch as P₂O₅, could considerably improve this in mineral compositionsespecially of the glass-wool type, while other oxides, such as alumina,seemed, on the contrary, to have a tendency to reduce it, at the veryleast in neutral pH. Reference may be made, for example, to PatentEP-412 878. However, a massive addition of P₂O₅ (or, for example, theomission of alumina) has not proved in the context of the invention tobe the most judicious approach. This is because other considerations mayarise, for example economic ones (P₂O₅ coming from expensive rawmaterials) and also technical ones—the changes in the proportions ofP₂O₅, and especially of alumina, in the composition may cause other ofits properties to vary in an undesirable or unknown manner. Thus, P₂O₅is not without influence on the viscosity of the composition, just likealumina. However, most particularly in the case of compositions of theglass-wool type to be fiberized by internal centrifuging, to which theinvention applies most advantageously, the viscosimetric behaviour ofthe composition is an important criterion to be suitably controlled.

The invention has therefore established a judicious compromise in thefollowing manner: the composition may contain P₂O₅, but in a moderateamount of at most 3 or 1.5%. Thus, its beneficial effect onbiodegradability is retained, without excessive addition which isexpensive and tends to increase the liquidus temperature of thecomposition.

By suitably adjusting the contents of the other main constituents of thecomposition, namely RO, R₂O, B₂O₃ and SiO₂, the Al₂O₃ content has, onthe other hand, been significantly increased, this being at least 16 to17%. The alumina content may thus advantageously be at least 18%,especially at least 19 or at least 20%.

It has been found that this combination allowed the biosolubilitycriteria, both measured in vitro tests in neutral pH and in in vitrotests in acid pH, to be satisfactorily met. Indeed, the matter ofknowing which pH is most representative of the in vivo physiologicalmedium, especially that of pulmonary regions, has not been definitivelyresolved. A high alumina content seemed up to now to be favourable torapid dissolution in acid pH, but slight/slow dissolution in neutral pH.

The invention makes it possible to obtain a high level of biosolubility,at least measured in vitro, whatever the pH, by selecting a high aluminacontent, but by adapting the content, especially of RO, R₂O and B₂O₃, soas to maintain its beneficial effect in acid pH without being made tosuffer in neutral pH.

The preferred CaO content of the composition according to the inventionis advantageously chosen between 4 and 11%.

In parallel, the preferred MgO content is chosen between 0.1 and 7%,especially between 0.3 and 6.5%.

In fact, it is usual to choose a CaO content which is higher than theMgO content, for a given total content of alkaline-earth metal oxides,especially for raw material cost reasons. The MgO content may thus bechosen to be very low or even zero (for example between 0 and 1%) or tobe higher, for example between 2 and 6%.

According to a first embodiment, the CaO/MgO ratio may thus be ≧1.25especially ≧5 and even ≧10.

However, it has proved useful, in the context of the invention, topropose a second embodiment consisting in providing MgO contentscomparable or even greater than CaO contents. MgO/CaO ratios may thus begreater than ≧0.8 or even greater than or equal to 1 or 1.05: this ratiowhich is different in the respective CaO and MgO contents, could have afavourable impact on the biodegradability of the composition.

The Na₂O content of the composition is at least 12%, especially between13 et 19.5%, while the preferred K₂O content is at least 0.5%,especially between 0.5 and 8%.

As in the case of the CaO and MgO contents of alkaline-earth metaloxides, in the case of alkali metal oxides the composition usually has amarkedly higher Na₂O than K₂O content. For a given total content ofalkali metal oxides, K₂O may thus have a very low or zero content (forexample, less than 3%, especially between 0.5 and 2.5%). However, it ispossible within the scope of the invention to also provide asignificantly higher K₂O content, for example about 5 to 7%, somethingwhich, for example, may represent up to more than one quarter or even ofmore than one third, by weight, of the total sum of the alkali metaloxides in the composition.

Advantageously, the composition contains alkaline-earth and alkali metaloxides in the following proportion: R₂O/RO>1.8 especially between 2 and4.

It should be noted that the sum SiO₂+Al₂O₃ allows the viscosimetricbehaviour of the compositions to be largely controlled: it is preferredfor this sum to be at least 60%, especially about 61 to 67%.

As regards the content of iron oxide (s) (total iron), this is optional,as mentioned above. The composition may have a low iron oxide content,added intentionally or as an impurity. Its presence in the compositionmay have a favourable effect on the fire behaviour of the mineral woolobtained.

Like iron, the presence of P₂O₅ in the composition is optional, it beingpossible for its content to be zero, or up to 0.1%, or at least 0.1% andup to 1.5 or 2%.

Boron oxide is an advantageous optional compound which acts especiallyas a fluxing agent, similar to the way in which the alkali metal oxidesact, and seems to be favourable to the biodegradability of mineral wool.Its presence furthermore tends to improve the thermal insulationproperties of the mineral wool, especially by tending to lower itsthermal conductivity coefficient in its radiative component.

The composition may furthermore contain a certain number of other minorcompounds, generally with a total content of at most 2 to 3% of thecomposition. These may, for example, be traces of TiO₂, MnO, SO₃, etc.

The temperature at which the compositions have a viscosity η (in poise)such that log_(η)=2.5, T_(log2.5), and/or the temperature at which ithas a viscosity η (in poise) such that log η=3, T_(log3). are/is greaterthan the liquidus temperature, T_(liq); the differenceT_(log2.5)−T_(liq) and/or T_(log 3)−T_(liq) is preferably at least 10°C., preferably at least 20 or 40° C. This difference defines the“working region” of the compositions of the invention, i.e thetemperature range in which they may be fiberized, most particularly byinternal centrifuging.

The mineral wools, as mentioned above, have a satisfactory level ofbiosolubility, whether the measurement method involves a neutral orslightly basic pH, or an acid pH.

The mineral wool according to the invention thus generally has a rate ofdissolution of at least 30, or at least 40 or 50 ng/cm² per hourmeasured at pH 4.5 and a rate of dissolution of at least 30 andespecially at least 40 or 50 ng/cm² per hour measured at pH 7.5.

In general, such mineral wool also has a rate of dissolution of at least30 and especially at least 40 or 50 ng/cm² per hour measured at the pH4.5 and a rate of dissolution of at least 30 and especially at least 40or 50 ng/cm² per hour measured at pH 6.9.

Generally, it also has a rate of dissolution of at least 60 andespecially at least 80 ng/cm² per hour measured at pH 4.5 and/or a rateof dissolution of at least 40 and especially at least 60 ng/cm² per hourmeasured at pH 6.9 or 7.5.

The mineral wool is mainly used to manufacture thermal and/or acousticinsulation products or soilless-culture substrates. The subject of theinvention is also any product comprising, at least partly, such mineralwool defined above.

Further details and advantageous characteristics will emerge from thedescription below of preferred non-limiting embodiments.

Table 1 below gives the chemical compositions, in percentages by weight,of nine examples.

Table 2 gives three other examples in which the accuracy of the chemicalanalysis is slightly greater and in which three physical characteristicsalso appear, namely the liquidus temperature (T_(liq)), the temperature(T_(log3)) at which the viscosity η expressed in poise is such that logη=3 and the temperature (T_(log2.5)) at which the viscosity η expressedin poise is such that log η=2.5, the three temperatures being expressedin °C.

When the sum of all the contents of all the compounds is slightly lessthan or greater than 100%, it should be understood that the differencefrom 100% corresponds to minor impurities/components which are notalways analyzed or cannot be analyzed in the trace state (TiO₂, SO₃)and/or is due only to the approximation, accepted in this field, in theanalytical methods used.

TABLE 1 EX. 1 EX. 2 EX. 3 EX. 4 EX. 5 EX. 6 EX. 7 EX. 8 EX. 9 SiO₂ 46.341.5 41 46 48.1 44.6 46.5 49.94 51.3 Al₂O₃ 19.9 19.6 20.1 18 16.9 19.517.6 17.3 16.5 CaO 5.1 10.1 7.9 5.8 4 8 5.9 5.1 5.2 MgO 0.5 0.3 3 6.16.1 2.3 4.4 2.2 3 Na₂O 19.4 19.0 13.8 17 13 13.6 16.7 13.7 12.7 K₂O 0.50.5 7.2 5 6 6.5 5.9 6.6 4.4 B₂O₃ 8.3 9 6 1.2 3.5 5 1.6 5.1 3.4 Fe₂O₃ — —0.9 1 1.5 0.6 1.4 0.6 2.0 P₂O₅ — — — — 1 0.0 0.0 0.0 1.6 Total 100 10099.9 100.1 100.1 100.1 100 100 100.1 RO 5.6 10.4 10.9 11.9 10.1 10.310.3 7.3 8.2 R₂O 19.9 24 21 22 19 20.1 22.6 20.3 17.1

TABLE 2 EX. 10 EX. 11 EX. 12 SiO₂ 46.35 49.38 49.64 Al₂O₃ 19.9 17.3 17.9CaO 5.1 5.1 7.8 MgO 0.04 2.2 2.7 Na₂O 19.4 13.7 16.6 K₂O 0.01 6.6 1.15B₂O₃ 8.95 5.05 4.15 Fe₂O₃ 0.02 0.6 0.01 P₂O₅ 0 0.04 0.01 TiO₂ — — 0.02SO₃ — 0.03 0.01 Total 99.77 100 99.99 RO 5.14 7.3 10.5 R₂O 19.41 20.317.75 T_(liq) 970 970 1050 T_(log3) 1072 1166 1139 T_(log2.5) 1183 12741242

The compositions are fiberized by internal centrifuging in a knownmanner, especially according to the teaching of the aforementionedpatents.

Their working ranges, defined by the difference T_(log2.5)−T_(liq), areamply positive.

Their biodegradability, especially measured at neutral or slightly acidpH (pH 4.9 or 7.5), or at acid pH (4.5) is satisfactory.

Examples 1 and 2 relate to a first embodiment of the invention, in whichthe greatly predominant oxide from the family of alkaline-earth metalsis CaO and the greatly predominant oxide from the family of alkalimetals is Na₂O.

Examples 3 to 9 relate to a second embodiment, in which, in contrast,the MgO content, from the family of alkaline-earth metals, and the K₂Ocontent from the family of alkali metals, respectively, are notinsignificant.

Examples 10 to 12, whose characteristics are specified more accurately,show that the compositions in question exhibit good characteristics formelting them (T_(liq) values not too high) and a working range wideenough for them to be processed by fiberizing without excessivedifficulty.

What is claimed is:
 1. A mineral wool capable of being dissolved in aphysiological medium, the mineral wool comprising the constituents belowin the following percentages by weight: SiO₂ 38-52% Al₂O₃ 16-23% RO(CaO + MgO) 4-15% R₂O (Na₂O + K₂O) 16-25% B₂O₃ 0-10% Fe₂O₃ (total iron)0-3%, P₂O₅ 0-3%, and TiO₂ 0-2%.


2. The mineral wool according to claim 1, wherein the mineral woolcontains between 4 and 11% of CaO.
 3. The mineral wool according toclaim 1, wherein the mineral wool contains between 0.1 and 7% of MgO. 4.The mineral wool according to claim 1, wherein the mineral woolsatisfies the relationship: MgO/CaO ≧0.8.
 5. The mineral wool accordingto claim 1, wherein the mineral wool satisfies the relationship: CaO/MgO≧1.25.
 6. The mineral wool according to claim 1, wherein the mineralwool contains at least 12% of Na₂O.
 7. The mineral wool according toclaim 1, wherein the mineral wool contains at least 0.5% of K₂O.
 8. Themineral wool according to claim 1, wherein the mineral wool satisfiesthe relationship: R₂O/RO>1.8.
 9. The mineral wool according to claim 1,wherein the mineral wool contains: SiO₂+Al₂O₃: at least 60%.
 10. Themineral wool according to claim 1, wherein at least one of(T_(log2.5)−T_(liq)) and (T_(log3)−T_(liq)) is at least 10° C.
 11. Themineral wool according to claim 1, wherein the mineral wool has a rateof dissolution of at least 30 ng/cm² per hour measured at pH 4.5, and arate of dissolution of at least 30 ng/cm² per hour measured at pH 7.5.12. The mineral wool according to claim 1, wherein the mineral wool hasa rate of dissolution of at least 30 ng/cm² per hour measured at pH 4.5,and a rate of dissolution of at least 30 ng/cm² per hour measured at pH6.9.
 13. The mineral wool according to claim 1, wherein the mineral woolhas at least one of a rate of dissolution of at least 60 ng/cm² per hourmeasured at pH 4.5, a rate of dissolution of at least 40 ng/cm² per hourmeasured at pH 7.5, and a rate of dissolution of at least 40 ng/cm² perhour measured at pH 6.9.
 14. The mineral wool according to claim 1,wherein the mineral wool is produced by a process comprising internalcentrifuging.
 15. Thermal insulation product, acoustic insulationproduct or soilless-culture substrate comprising, at least in part, themineral wool of claim
 1. 16. A method of making a mineral wool, themethod comprising fiberizing a mineral composition; and forming themineral wool of claim
 1. 17. The method according to claim 16, whereinthe fiberizing comprises internal centrifuging.